The invention relates to a direct bit drive for deep drilling tools.
It is known to provide a direct bit drive for deep drilling tools comprising a housing having an inlet end and an outlet end, a rotor disposed in said housing for rotation therein and for limited radial enlargement but not for axial displacement, said rotor and said housing interengaging at surfaces shaped in the manner of helical teeth, said shaped surfaces jointly defining at least one helical working space for a liquid or gaseous working medium, one of said shaped surfaces being formed on a shaped member of resiliently deformable material, and bearing in regions which move axially, upon relative rotary movement between said housing and said rotor, under pressure, with a sealing action, against the other shaped surface, which is of rigid construction, said shaped member of resiliently deformable material being arranged to be acted upon by the pressure of a pressure medium in a pressure chamber with radially directed deformation forces which alter, depending on the pressure prevailing in the working medium at the inlet side of said housing, and wherein said rotor comprises a shaft which acts as a carrier for the shaped member of resiliently deformable material, said shaped member of resiliently deformable material being disposed on the shaft and being constructed in the form of a diaphragm member which is located at its two ends on the shaft and is freely displaceable radially in its intermediate region, relative to the shaft, and which, at its inside, during its radial displacement movements, is in positive guiding engagement with formations of the shaft and can be acted upon by the pressure of a pressure medium in a pressure chamber formed between the shaped member of resiliently deformable material and the shaft with said radially directed deformation forces.
Such a direct bit drive forms the subject of an earlier proposal. By the earlier proposal, a direct bit drive based on the Moineau principle is provided for deep drilling tools, wherein the contact pressure which determines the sealing action between the regions of the shaped surfaces which are in engagement can be adapted to the pressure and temperature conditions of the working medium and can be adapted so that under all operating conditions, the required sealing is retained and on the other hand the wear is reduced to a minimum extent. Wear phenomena are immediately compensated for by the resilient expansion of the shaped member. Apart from this, as a result of its association with the shaft as the inner component, the shaped member forms a relatively simple wearing part which can easily be replaced if necessary. The deformation of the shaped member, which is made radially variable as a whole in practice, is very precise in all regions in operation of the direct bit drive according to the earlier proposal, and is uniform, with simultaneous securing of a satisfactory transmission of torque between shaped member and shaft over their length and periphery. The adaptation which can be effected in operation ensures not only a running of the direct bit drive under optimum working conditions but also eliminates the necessity of providing a multiplicity of types of machines of different design in order to make allowance for the particular operating requirements. In addition, high performances can be achieved with the direct bit drive according to the earlier proposal, with a considerably reduced structural size and correspondingly reduced costs, because even with a construction with single-thread helical teeth of housing and shaft, that is to say of stator and rotor, pressure differences between inlet and outlet of the working chamber of the order of magnitude of 120 bar and more can be achieved with a high volumetric efficiency. When the direct bit drive according to the earlier proposal is used under normal drilling conditions, this can be constructed for example with nine-thread helical teeth, in a length of about 1 m, and such a drive delivers a considerably higher torque than conventional direct bit drives which have a structural length of about 3 to 4 m for normal drilling conditions.
The object of the invention is to provide a direct bit drive of the kind indicated which has a long life of its axial bearings when designed for high performances.